GeoJeepCachers

We are coming to the island November 6th, 2015. We have a Garmin GPSmap 62st and a Magellan explorist GC. I can't figure out how to get the maps of the island on to them so that we can use them. Suggestions? What do you use? Will ours work? Should we just by a device when we get there? HELP! I can't do without geocaching for 3 years!!!